Animals examined as part of the study include deep-ocean sea cucumbers, urchins and brittle stars.

You will often find species of shrimp living on urchins and starfish in the tropics and, if you look carefully, might also find very small hermit crabs adopting the same behaviour, particularly on starfish.

Origin

An urchin was originally a hedgehog, and the name, based on Latin hericius ‘hedgehog’, is still used in some English dialects. People started applying urchin to poor, raggedly dressed children in the mid 16th century, though this did not become common until more than 200 years later. As a name for a marine invertebrate sea urchin comes from the original sense, referring to the spines on its shell.